There is known a sewing machine which images a workpiece on a needle plate using an optical element fixedly mounted on the frame of the sewing machine, obtains the amount of movement of the workpiece from the imaged data, and controls a sewing machine motor so as to perform a needle drop according to a predetermined movement amount, thereby maintaining a sewing pitch at a set value (see, for example, JP-B-4724938 and JP-A-2006-517449)
However, the above conventional sewing machine obtains the workpiece movement amount and controls the sewing machine motor so as to perform the needle drop when the workpiece is moved at the set sewing pitch.
Thus, even when there is generated an error in an actually formed seam with respect to the set sewing pitch, this error cannot be corrected, thereby raising a fear that the sewing can be continued with the error uncorrected.